Combustion air supply through grates and grate construction



May 15, 1956 J. J. MARTIN 2,745,364

COMBUSTION AIR SUPPLY THROUGH GRATES AND CRATE CONSTRUCTION Filed Sept.28, 1949 i a Sheets-Sheet 1 a in 7 25 /2 "9 y 1956 J. J. MARTIN2,745,364

COMBUSTION AIR SUPPLY THROUGH GRATES AND GRATE CONSTRUCTION Filed Sept.28, 1949 3 Sheets-Sheet 2 INVENTOR L/ZJE/v/w': Jd JEF Mwr/A/ BY/(JALATTORN May 15, N56 J. J. MARTIN 2,745,354

comaus'rzom AIR SUPPLY THROUGH GRATES AND GRATE CONSTRUCTION Filed Sept.28, 1949 5 Sheets-Sheet 3 iifiglk INVENTO R Joly/W55 c/ZJifW87/A4 BY WflW ATTORNE U ed S e Pw COMBUSTION AIR SUPPLY THROUGH GRATES AND GRATECONSTRUCTION The present invention relates to an'improved method ofsupplying combustion air through fuel-burning grates and particularlythe individual bars thereof, and to the construction of suchgrates andelements or grate bars therefor.

With the conventional operating'methods and constructions offuel-burning grates, removal of the heat trans- 2,745,364 PatentedMay.15, 1956.

or transverse ribs and the air may be additionally thronice ' tled atthe end of the channels before entering the dis:

ferred to the grate elements by radiation and contact'f particularlywhen burning fuel of high heat value or when operating with highlypreheated air, is difficult and the life of the grate bars is short.

For better cooling of the grate, narrow bat-shaving high cooling ribshave been used. Since the amount of air available perunit of gratesurface is limited, agrate fuel spread on the grate. The flow of airtherefore de-' pends chiefly on the resistance of the fuel layer, and,at portions of the grate which are covered by liquid slag, the flow ofair is much reduced or completely interrupted, sothat the grate isoverheated and damaged.

Conventional methods and constructions do not produce a flow of airwhich assures continuous and efiicient cooling of all parts of the grateand which is independent of'the different conditions of the fuel layerat various portions of the grate. ance of the fuel layer to the flow ofair is low, the velocity of the air flowing underneath and at the flanksof the grate bars is not more than 9 to 15 feet per second and the heattransfer is therefore insuffieient. Only at the flanks where the airleaves the slots between the bars, the heat transfer is somewhatgreater, but these surfaces are too insignificant to efiect appreciablecooling.

Although the temperature of the grate bars of conventional grates issometimes higher than 1500 degrees Fahrenheit, the temperature increaseof the air is not much more than, say, 200 degrees Fahrenheit, and thecooling efiect is insufiicient.

It is an object of the present invention to provide an improved methodof operating and an improved construction of grates consisting of aplurality of bars, wherebythe heat transfer from the grate to thecombustion air is substantially increased at all parts of the grate,and, not only wear and the cost of upkeep is reduced, but also thetemperature of the air reaching the fuel is considerably increased,greatly improving combustion conditions According to the invention allor at least a large portion of the air does not just pass along thegrate bars but is conducted through cavities in the individual bars athigh velocity and in streams moving back and forth and may be furtheraccelerated to a predetermined degree at the points of its dischargeinto the fuel. For this purpose, one or more channels are provided onthe under: side of the bars which are formed by suitable longitudinalEven at portions where the resistcharge openings toward the fuel layer.All this causes a highly turbulent flow of the air, which is due to thegreat pressure reduction and efiects not only efiicient cooling of thegrate bars but aslo stabilization of the combustion process .byequalization of the air flow to.the various zones of the fuel bed; thiseffects better drying ofQthe fuel and improved ignition particularly ifwet and low grade coals are burned.

Further and other objects of the present invention will be hereinafterset forth in the accompanying specification.

and claims, and are shown in the drawings which, by way of illustration,show. what I now consider to be preferred embodiments of the invention.In the. drawings: V v v I Fig. 1 is a longitudinal part sectional viewthrough a step grate according to the invention; v

Fig. 2' is a bottom view of a grate bar according. to the invention witha portion of the .cover plate removed;'

Fig. 3 is a cross-section of the grate bar shownin Fig. 2, the sectionbeing taken along line IlIIII of Fig.2; e 7

Fig.4 is a bottom view of a modified grate bar according to theinvention with the cover plate removed; I

Fig...5 is a cross-section of the bar shown infFig. 4

I F taken along line V Y- of Fig. 4; V

' Fig. 6 is a bottom view of a further modificationof threejuxtapositioned grate bars according to. the I inven: tion with thecover platesremoved;

'Fig. T is. a cross-section through. the bars showninf Fig. 6 takenalong line VII-VII of said figure; j i

I Fig. 8 is a bottom view of still another modification of a grate baraccordingto the invention with a part of the cover plate removed;

Fig. 9 is a cross-section of the bar shown in Fig. 8 taken along lineIX-IX of said figure;

Fig. 10 is a bottom view of another modification of threejuxtapositioned grate bars according to the invention with the coverplates removed;

Fig. 11 is a cross-section through the grate bars shown, in Fig. 10taken along line XIX[;

Fig. 12 is a bottom view of still, another modification of a grate baraccording to the invention with the cover plate removed;

Fig. 13 is a cross-sectionof the bar shown in Fig. 12

taken along line X[IIX[II of said figure; v

' Fig. 14.is a diagrammatic bottom view of three juxtapositioned gratebars provided with hold-down means ac-.. cording to the invention; I f

Fig. 15 is a cross-section of the gratebars shown in Fig. 14 takenalongline XV-XV of Fig. 14.

Fig. 16 is a diagrammatic longitudinal sectional view of a modifiedgrate bar construction according .tothe invention; I

Fig. 17 illustrates in top .view a grate bar arrangement. according tothe invention; 7 p

Fig. 18 illustrates in top view the grate bar arrangement shown in Fig.'1;

Fig. l9 is a longitudinal sectional view. of a further modification of agrate bar construction according to the invention; V

Fig. 20 is a sectional view of the grate bar shown in Fig. 19 takenalong line XXXX and looking in the direction of the arrows inFigure 19;V

Fig. 21 is a bottom view of the cover plate used inthe constructionshown in Figs. 19 and 20.

Like parts are designated by like numerals in all figures of thedrawings.

In the embodiment of the invention shown in Figures 1 to 9, theunderside of the grate bars 1 isprovided with a plurality of walls orbafiies 20 forming channels or conduits 3 which may be either fully castin the bars or open at one side and covered by a plate 10, asillustrated. The plate 10 which forms the bottom wall of the grate barmay be cast of a material having the same heat expansion coeflicient asthe grate bars or may be made of annealed sheet iron spot-welded to thegrate bars either at its circumference and/or in the center throughholes positioned adjacent to the ribs, and its ends may rest slidably onsuitable supports 22 to permit expansion as shown in Fig. 16.

Instead of providing four parallel channels longitudinally of the grateelement, as shown in Figures 2 and 3,,

three adjacent parallel conduit portions may be arranged as shown inFigures 4 and 5. In the first case, the air enters at 16 through anopening in the bottom of the front portion of the bar, and in the lattercase the air enters through an opening 17 in the side wall atthe rearportion of the .bar. The flow of the air is indicated by fine lines andarrows in the drawings.

In the modification illustrated in Figures 6 and 7, two longitudinalchannels only are provided, and the air enters through openings 18 inthe bottom of the front end of the bar.

Instead of introducing the air at one side of the bars and conducting itin a meandering conduit to the other side as in Figures 1 to 7, the airmay enter in the middle of the bar. and move in two symmetricalserpentine streams toward both sides of the bar as shown in Figures 8and 9.

The channels may be superimposed as shown in'Figures 10 and 11 insteadof juxtapositioned as per Figures 1 to 9.

Baflies 21 may be arranged transversely to the longitudinal axis of thebars and extend only over a part of the width of the bars as shown inFigures 12 and 13, whereby the air stream is forced to. asume ameandering configuration.

It is desirable to increase the flow area of the conduits in accordancewith the increase in the volume vof the air due to heating This isindicated in Figure 12.

In order to prevent flow of incoming cool air alongside the grate barsand into the stream of hot air leaving an element, the recesses 23 inthe side walls or the passages 14 at the bottom of thegrate bars inwhich the cool air flows to the air inlet are separated from therecesses through which the hot air leaves the'bars, by sealing ribs orair flow blocking means 4 projecting laterally from the side walls ofthe grate bars. From the rib 4 a horizontal rib extends along thelongitudinal upper edge of the grate bar which horizontal rib incooperation with the adjacent horizontal rib of a juxtapositionedgratebar constitutes also a means for blocking air flow between the barsso that the air must flow through the bars. 9 leaking between thesealing ribs assumes high velocity, 60 to 140 feet per second, andcontributes eflfectively to the cooling of-the ribs. This leakage airunites at the air outlets with the main air streams 12.

Air discharge recesses 13 may be provided in both side walls of thegrate bars as shown in Figures 1 to' and 8 i and 9 or on one side onlyas in Figures 6 and 7 and to 15 where they are designated by numeral 19.

The flow of'hot air leaving the internal channels 3 may be substantiallyso guided that it cannot escape other than by flowing olf to the fuellayer 2 at the air discharge zone 5 formed. by adjacent bars.

However, an arrangement may also be provided in such a manner that theair leaving the channels 3 of each bar may flow ofi in part at saiddischarge zone 5 and in part enter a chamber 14, the bottom of which isformed by the top of the underlying bars, the transverse direction ofThe air stream the chamber 14'. This arrangement permitsintercommunication of air heated in several bars ofv the same step ofthe grate. It equalizes air flow through all elements of one step andalso. assures cooling of those elements whose proper air discharge isblocked, for example, by liquid slag. I v

The web 4' may form an integral part of the grate bar 1; it can,however, also be attached to or form a part of the cover plate 10', asshown in Figs. 19 and 21.

The superimposed bars of a grate maybe in alignment, as shown in Fig.17, so that the air outlets 13 of superimposed bars are all placed inthe same verticaluplane; or they may be offset by one half of theirwidths,;as shown in Fig. 18, for distributing the air in the fuel moreequally;

With this novel manner of admitting air to the fuel through the gratebars, the number of points where air is admitted to a given zone can bemademuch smaller and the velocity of the air can be made much greaterthan in conventional grates. The invention is not limited to theillustrated application to stoker grates but may be used.

as well in plane grates and chain grates.

Due to the high velocity of the 'air in a grate according I to theinvention which is substantially independent of the.

resistance to air flow caused by the fuel layer, the grate bars andclearances therebetween are kept cleaner than is This cleaning effect.

possible with conventional systems. can be further improved by agradually downward'widening of the nozzle spaces between relativelymoving bars as is indicated in Figures 3, 5 and 7, i. e. by'u'pwardly,

diminishing the depth of the recesses 13-. The sealing webs 7 (Fig; 6)of movable bars are preferably made thicker than those (4) of thejuxtapositioned bars to such an extent that they have a closing effectduring the whole relative movement of the bars.

In order to prevent rising of individual bars due to heat expansion andeventual warping, hold-down projections'8 may be provided which extendunder the side walls of the small number of discharge nozzles throughwhich the air flows at high velocity, cause heat absorption by thecombustion air and consequently cooling of the grate which coolingis-considerably increased relative to the conditions in conventionalgrates where the air flows in one direction only in open channels anddirectly'into the fuel.

Due to the increased length and reduced'flow-area of the conduitsthrough which the air passes in a grate according to the invention, agreat pressure drop amounting to 4 inches of water and more is producedin each grate bar which considerably exceeds the pressure drop in thefuel bed which is only 1.1 to 2.4 inches of water, so that the amount ofair passing into the fuel is practically independent of changes in theresistance of the fuel to air flow. This improves combustion and makesit uniform in all zones of the grate; it also increases the dryingeffect of the air and improves ignition, particularly when damp and lowgrade fuel is burned.

With the system according to the invention and normal air flowresistance of the fuel bed, only a small portion of the initial pressureof the air, say 8 inches of water, is.

say 10 to 15 per cent, and no craters are formed in the fuel bed. Thisis of particularimportance with coarse-.

grained fuels which offer little resistance to air flow, as

well as with coal having a tendency to develop an aero dynamicallyunstable layer.

On the .other hand, if there is a tendency to increase air resistance ofthe fuel 'layer on top of a grate bar, the

throttling efiect f the bar is considerably reduced and the air pressureavailable for piercing through the fuel is correspondingly increased andcombustion of the flowresisting portion of the fuel layer sped up. Withthe system according to the invention, the range of fuel which can beefiiciently burned is widened with regard to the size and shape of thegrain, as well as with respect to the fusing point of the fuel.

If the increase of the air flow resistance of the fuel layer extendsover whole zones of the grate or large portions thereof, the airpressure under the zones increases due to the characteristic of theair-blower which causes quick return to normalcy of the air supplyconditions in the fuel layer.

The higher combustion air temperature caused by the system according tothe invention improves drying and ignition of damp fuel or of fuel oflow heat value. A grate according to the invention has a heataccumulating and recuperative effect, and if the character of the coaltends to interrupt combustion locally and the fire must be forcedtemporarily, the heat accumulated in the grate is quickly transferred tothe coal whereby the ignition temperature is maintained, combustion isstabilized, reliable combustion of low heat value fuels is assured, andthe heat liberated per unit of grate surface is increased.

While I believe the above described embodiments of my invention to bepreferred embodiments, I wish it to be understood that I do not desireto be limited to the exact details of method, design and constructionshown and described, for obvious modifications will occur to a personskilled in the art.

I claim:

1. A fuel burning grate receiving combustion air from below the grateand comprising a plurality of juxtapositioned longitudinal hollow gratebars, each of said grate bars having a forward and a rearward portion,each of said grate bars having an air inlet opening and two parallelside walls, an air discharge opening in at least one of said side wallsat the forward portion of the grate bar, and air flow blocking meansprojecting laterally from at least one of said side walls in the rear ofsaid discharge opening, said air flow blocking means of one of twoneighboring grate bars being adjacent to the other grate bar and beingadapted to block flow of air between the neighboring bars all along thelength of the neighboring bars in the rear of said discharge opening,said blocking means leaving an air flow passage between the side wallsof the forward portions of two neighboring grate bars, said passagereceiving air from the inside of the grate bar through said dischargeopening.

2. A fuel burning grate according to claim 1, in which said air flowblocking means include a rib extending substantially transversely to thelongitudinal extension of the bar.

3. A fuel burning step grate receiving combustion air from below thegrate and comprising a plurality of stepwise superimposed rows ofjuxtapositioned longitudinal hollow grate bars, eachof said grate barshaving a forward and a rearward portion, the forward portions of a rowof juxtapositioned bars resting on top of the rearward portions of theunderlying row of grate bars, each of said grate bars having an airinlet opening and having two parallel side walls and a bottom wall, anair discharge opening in at least one of said side walls at the forwardportion of each grate bar, and air flow blocking means projectinglaterally from said side walls and downwardly from said bottom wall andincluding portions extending transversely to the longitudinal axis ofsaid grate bars, said blocking means, being in the rear of said airdischarge opening and forward of said inlet opening, said air flowblocking means projecting laterally from the side walls of a bar beingadjacent to the juxtapositioned bar and said air flow blocking meansprojecting downwardly from the bottom wall of a bar being adjacent tothe top of an underlying grate bar, said air flow blocking means beingadapted to block flow of air between neighboring and superimposed barsall along the length of the neighboring and superimposed bars in therear of said air discharge opening, said blocking means leaving an airflow passage between the side walls of two neighboring grate bars at theforward portion of said grate bars, said passage receiving air from theinside of the grate bar through said discharge opening.

4. A fuel burning grate as defined in claim 3, in which said grate barshave a forward wall having a bottom surface resting on the underlyinggrate bar, said forward Walls of a plurality of juxtapositioned gratebars forming with the air flow blocking means projecting downwardly fromthe bottom walls of a plurality of juxtapositioned grate bars and withthe bottom Walls of the forward portions of a plurality ofjuxtapositioned grate bars and with the tops of the rear portions of aplurality of underlying juxtapositioned grate bars an air chamberextending transversely of the longitudinal axes of the grate bars andreceiving air from a plurality of air discharge openings, equalizing thepressure in said air flow passages.

References Cited in the file of this patent UNITED STATES PATENTS641,124 Lee Jan. 9, 1900 1,481,366 Herkenrath Jan. 22, 1924 1,513,987Hare Nov. 4, 1924 1,925,840 Marx Sept. 5, 1933 FOREIGN PATENTS 103,999Germany July 12, 1899 104,822 Austria Nov. 25, 1926 110,389 Germany May10, 1900 370,781 Germany Mar. 7, 1923

